As compounds which release photographically useful groups in correspondence to image density during development, there are known hydroquinone derivatives (the so-called DIR hydroquinones) which release development inhibitors in proportion to image density, those which release solvents for silver halides in proportion to image density and those or sulfonamide phenol derivatives which release diffusive dyes in proportion to the amount of the silver developed.
Examples of compounds heretofore known as DIR hydroquinones include those described in U.S. Pat. Nos. 3,379,529, 3,620,746, 4,377,634, and 4,332,878 and Japanese Patent Application (OPI) No. 129536/74 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application) corresponding to U.S. Pat. No. 3,930,863. As hydroquinone derivatives which release solvents for silver halides, those described, e.g., in U.S. Pat. No. 4,459,351 are known. As hydroquinone derivatives which release diffusive dyes, those described, e.g., in U.S. Pat. Nos. 3,698,897 and 3,725,062 are known, and as sulfonamide phenol derivatives having the same property as the hydroquinone derivatives, those described, e.g., in the The Journal of Organic Synthetic Chemistry, (Japan), Vol. 39, p. 331 (1981), Kagaku-no-Ryoiki, Vol. 39, p. 617 (1981), Kino Zairyo, Vol. 3, p. 66 (1983), Photogr. Sci. Eng., Vol. 20, p. 155 (1976), Angew. Chem. Inter. ed. Eng., Vol. 22, p. 191 (1983), The Journal of Organic Synthetic Chemistry, (Japan), Vol. 40, p. 176 (1982), and The Japan Chemical Industry Association, Monthly, Vol. 35 (11), Vol. 29 (1982) are known.
Although the hitherto known compounds described in the above references have a large variety of applications depending on the photographic effects of photographically useful groups released, the function required for the redox center conducting redox reaction, reduction and oxidation reaction, by which the photographically useful groups are released has many common features. In other words, as a matter required for the overall photography of these days, steady obtaining with promptitude and ease of a picture of high quality is becoming more and more important, which results from the fact that these compounds are used as elements to achieve such objects or to effect auxiliary action. It can be said, therefore, that the performance required for these redox centers is how the photographically useful groups can be released quickly, in a short time, in good timing and efficiently.
The performance required for these redox centers will be described in more detail as follows.
First, the rate at which these redox centers effect cross redox reaction with the oxidant of a developing agent or of an auxiliary developing agent produced during development or that at which they themselves are changed to oxidants by reducing silver halides and other silver salts should be sufficiently high, in order that they may exhibit sufficient activity during the development processing.
Secondly, the photographically useful groups should be released from the oxidants of the redox centers thus produced very rapidly and efficiently.
Thirdly, these redox centers should be so stable during storage that they are not decomposed by oxygen in the air or by other substances so as to adversely affect photographic utility.
As for the first aspect, it is considered that acceleration of the rate at which the redox centers are oxidized can generally be accomplished by lessening their oxidation potential. However, as described in Journal of American Chemical Society, Vol. 60, p. 2084 (1938), if the oxidation potential is lessened, the rate at which the redox centers are oxidized by oxygen in the air will generally be increased, which gives an unfavorable effect from the third point of view. Therefore, it is difficult to aim at coexistence of rapid preservation of the function during the processing and the stability of the redox centers during the storage by lessening the oxidation potential.
On the other hand, measures are sometimes taken to protect the redox center from the standpoint of preventing oxygen in the air from oxidizing it. Such measures can be taken with relative effectiveness when the pH of the developer is high, when remarkable accelerating effect by the composition of processing solution described in Japanese Patent Application (OPI) Nos. 197037/84, 201057/84 (EP 125523A) can be ideally utilized, or when the processing time is very long. However, the protection of the redox center will generally result in a somewhat longer time being needed from the start of the development to the exhibition of the desired function because one or more additional reaction steps are required for the redox center to exhibit its function, often leading to adverse effects on a sufficient exhibition of the function. Considering the fact that further accelerated processing speeds will be desired in future, there seems to be many difficulties in aiming at the coexistence of a sufficient exhibition of the desired function with the stability of the redox center during storage.
As for the second viewpoint, the heretofore known compounds described in the above cited patents are not fully satisfactory with respect to the rate and efficiency at which the photographically useful groups are released from the oxidant of the redox center. Thus, the exhibition of the desired function may be thought to be greatly promoted if the rate and efficiency could be raised.